1. Field of the Invention
This invention relates to a pneumatic tire and more particularly to a heavy duty pneumatic radial tire for use in, for example, construction vehicles comprising a pair of bead portions each including a bead core embedded therein, a radial carcass of a rubberized cord ply extending between the pair of the bead portions and wound around each bead core from the inside of the tire toward the outside thereof, a belt superimposed about a crown portion of the carcass and comprised of at least one belt layer, and a tread disposed on an outside of the belt in the radial direction.
2. Description of Related Art
In the conventional heavy duty pneumatic radial tire, the bead core is at a horizontal state in an axial direction of the tire or a tapering angle .theta..sub.C of an inner side of the bead core in the radial direction is zero. A bead base of the bead portion is tapered so that an inner diameter of a bead base face is gradually decreased from a bead heel part toward a bead toe part. In this case, a tapering angle .theta..sub.B of the bead base in the tire is somewhat larger than a tapering angle .theta..sub.R of a bead seat in a rim and is set to a degree of (.theta..sub.R +.alpha.), whereby a tightening margin is held between the tire and the rim.
In such a conventional tire, when a large torque is applied to the tire, slippage is caused between the bead base portion of the tire and the bead seat of the rim and hence there is a tendency that rubber beneath the bead core, particularly rubber in a bead heel part is worn to easily cause a trouble of air leakage.
This is due to the fact that since the inner side of the bead core in the radial direction is parallel or substantially parallel to the axial direction of the tire and the bead base of the bead portion is tapered, the pressure to the bead heel part becomes high and the pressure to the bead toe part becomes small and hence rubber is worn at the side of the bead heel part subjected to a high pressure.